Multiplexer

A multiplexer (MUX) is a device that selects one of several analog or digital input signals and forwards the selected input to a single output line, with the selection controlled by one or more select input lines.^[1] These devices function as data selectors, enabling efficient routing of information in electronic systems by allowing multiple sources to share a common output path.^[2] Multiplexers come in various configurations based on the number of inputs, such as 2-to-1, 4-to-1, 8-to-1, and larger variants, where the number of select lines required is determined by the logarithm base 2 of the input count.^[3] They can implement Boolean functions and are constructed using logic gates like AND, OR, and NOT, or as integrated circuits for practical use. Analog multiplexers, built with relays or transistor switches, handle continuous signals, while digital ones process discrete binary data.^[2] In applications, multiplexers play a critical role in central processing units for instruction decoding and data path control, as well as in graphics controllers for signal selection in display systems.^[4] They are essential in telecommunications for multiplexing multiple channels onto a single transmission line, in computer memory systems for address decoding, and in global positioning systems (GPS) and audio/video processing for efficient signal management.^[5]

Basic Principles

Definition and Purpose

A multiplexer, often abbreviated as MUX, is an electronic device or circuit that selects one of several analog or digital input signals and forwards the chosen signal to a single output line based on control or select signals.^[6][7] This selection process enables the device to act as a digital switch or analog signal router, distinguishing it from other combinational logic elements by its focus on input channeling.^[8] The primary purpose of a multiplexer is to enable efficient signal routing, data selection, and resource sharing in electronic systems, such as communication networks where multiple channels share a transmission medium and computing hardware where inputs are prioritized for processing.^[6][9] In contrast, a demultiplexer performs the inverse function by distributing a single input signal to one of multiple output lines.^[10] The concept of multiplexing originated in 19th-century telegraphy and early telephony, where techniques like time-division multiplexing were developed to combine multiple signals over shared lines, with electronic multiplexers emerging in the mid-20th century alongside transistor-based circuits for more precise control.^[11][12] At a high level, a multiplexer's structure includes $2^m$2m input lines, $m$m select lines that determine the active input through binary addressing, and a single output line that carries the selected signal.^[13] Multiplexers handle both analog signals via switch arrays and digital signals via logic gates, though detailed implementations vary by type.^[9]

Operational Mechanism

The operational mechanism of a multiplexer relies on control lines, also known as select lines, which decode binary values to activate a single input path to the output while isolating all others, effectively routing one of multiple inputs to a single output.^[14] For instance, in a 4:1 multiplexer, two select bits (S1 and S0) are used to choose among four inputs, where the binary combination on the select lines determines which input is connected to the output via internal switches or logic gates.^[15] A basic 2:1 multiplexer illustrates this process with two inputs (I0 and I1), one select line (S), and output Y, where Y equals I0 when S=0 and I1 when S=1.^[16] The truth table for this configuration is as follows: This behavior can be expressed using Boolean logic as $Y = \bar{S} \cdot I_0 + S \cdot I_1$Y=Sˉ⋅I0​+S⋅I1​, analogous to a switch that toggles between inputs based on the select signal.^[17] In general, for a $2^m$2m-to-1 multiplexer with $m$m select lines, the output is given by $$Y = \sum_{k=0}^{2^m - 1} I_k \cdot D_k$$Y=k=0∑2m−1​Ik​⋅Dk​ , where $D_k$Dk​ represents the decoded select signal that is high (1) only for the selected input index k and low otherwise.^[15] Signal integrity in multiplexers is preserved by minimizing crosstalk between channels through techniques such as physical isolation in the layout and by accounting for propagation delay, which is the time interval from a change in select lines to the corresponding output transition.^[18]

Analog Multiplexers

Design Characteristics

Analog multiplexers employ transmission gates as core components, typically constructed from complementary pairs of NMOS and PMOS MOSFETs to enable bidirectional signal flow with minimal voltage drop. These gates provide low on-resistance, often below 1 Ω, and high off-isolation exceeding hundreds of megohms, ensuring efficient signal routing while preventing leakage between channels. In earlier designs, electromechanical relays were used to achieve comparable low on-resistance and superior off-isolation, though they suffered from slower switching and higher power demands compared to modern semiconductor implementations. Key characteristics of analog multiplexers include bandwidth limitations determined by the interaction of on-resistance and output load capacitance, typically resulting in -3 dB bandwidths from tens to hundreds of MHz depending on the device and load. Channel crosstalk, quantified in decibels, measures unwanted signal coupling between channels and is usually specified at -70 dB or better for audio frequencies to minimize interference. The on/off resistance ratio enhances signal integrity by isolating inactive channels, while nonlinearity effects such as total harmonic distortion (THD) are critical for applications involving AC signals, with typical THD values below 0.01% at 1 kHz. Analog multiplexers are categorized as single-ended, where inputs share a common ground reference, or differential, which handle balanced signals between two lines for improved noise rejection and common-mode voltage tolerance. Voltage multiplexers process voltage-based signals directly through the switches, whereas current multiplexers steer current signals, often requiring careful design to manage compliance voltages and avoid saturation. Performance metrics emphasize fast switching speeds, generally in the range of nanoseconds to microseconds for turn-on/turn-off times, enabling rapid channel selection without significant settling delays. Power consumption is low, often in the microwatt range for CMOS devices, supporting battery-operated systems. Temperature stability is another factor, with on-resistance varying by up to 50% over -40°C to 85°C operating ranges, necessitating compensation in precision applications. For instance, the MAX4638 8:1 analog multiplexer achieves a -3 dB bandwidth of 85 MHz with low leakage currents. Historically, early integrated analog multiplexers emerged in the late 1960s, with devices like the CD4051 CMOS 8:1 multiplexer introduced for audio and video signal switching, marking a shift from discrete components to monolithic ICs.

Common Applications

Analog multiplexers play a crucial role in data acquisition systems by enabling the sequential sampling of multiple analog sensors through a single analog-to-digital converter (ADC), thereby reducing system complexity and cost. For instance, in oscilloscopes, they facilitate the multiplexing of multiple input channels to the ADC, allowing efficient capture of various signals without dedicated converters for each channel. This approach is particularly valuable in high-channel-density setups, where performance optimization involves careful selection of multiplexer settling time and on-resistance to maintain signal integrity across channels.^[19][20] In audio and video switching applications, analog multiplexers route continuous signals with minimal distortion, ensuring high-fidelity transmission in devices like audio mixers and AV selectors. Buffered multiplexers, for example, are designed for video frequencies, offering low differential gain and phase errors to preserve signal quality during switching. These components support applications requiring high-speed operation and low power, such as composite video routing, where crosstalk must be minimized to avoid interference between channels.^[21][20][22] Within instrumentation, analog multiplexers are integral to multimeters and telemetry systems for industrial monitoring, where they select among various analog inputs to enable precise measurements. In handheld digital multimeters, for example, a precision analog multiplexer controls resistor divider networks to configure input ranges, supporting low-power operation and high accuracy in voltage and current sensing. Telemetry applications in industrial settings use these devices to aggregate sensor data from remote locations, facilitating real-time monitoring with reduced wiring complexity.^[23][20] In automotive and medical domains, analog multiplexers handle signal selection for critical analog inputs, enhancing system reliability. Automotive electronic control units (ECUs) employ them to connect multiple switch inputs and sensors to a microcontroller, as seen in body control modules managing functions like lighting and wipers, where robustness against voltage transients is essential. In medical patient monitors, they enable multiplexing of bio-signals such as ECG and bioimpedance in multiparameter devices, supporting high-precision AC and DC measurements for vital signs monitoring.^[24][25][26] A modern trend since the 2010s involves integrating analog multiplexers into Internet of Things (IoT) devices for sensor fusion, where multiple environmental or physiological sensors are combined to provide comprehensive data insights. This integration allows compact, low-power systems to process diverse analog signals efficiently, as in wireless sensor networks that fuse data from arrays for applications like environmental monitoring or wearable health tracking. Such advancements leverage precision multiplexers to minimize power consumption while enabling scalable sensor interfacing in edge computing scenarios.^[20]

Digital Multiplexers

Logic-Level Implementation

Digital multiplexers at the logic level are constructed using combinational logic gates such as AND, OR, and NOT gates. The simplest form is the 2:1 multiplexer, which selects between two inputs, I0 and I1, based on a single select input S. The output Y is given by the Boolean expression: $$Y = (S \land I_1) \lor (\lnot S \land I_0)$$Y=(S∧I1​)∨(¬S∧I0​) This implementation requires two AND gates, one NOT gate, and one OR gate.^[27] For larger multiplexers, such as an n:1 configuration, a decoder-based approach is commonly used. An n-bit decoder generates 2^n unique minterms from the select inputs, and each input line is ANDed with the corresponding decoder output before all results are ORed together to produce the final output. This structure ensures only one input is enabled at a time.^[27] The operation of a 4:1 multiplexer can be illustrated through its truth table, which shows the output Y for all combinations of the two select bits S1 and S0, with inputs I0 through I3. The table is as follows: This table confirms that the select bits determine which input propagates to the output.^[27] Timing considerations in logic-level implementations are critical for performance. Propagation delay, the time from input change to output stabilization, varies by logic family. In TTL-based multiplexers like the 74LS151, typical propagation delay is around 10-16 ns, enabling operation above 10 MHz. In contrast, CMOS implementations such as the 74HC151 exhibit delays of 14-25 ns at 5 V supply, supporting lower power but potentially slower speeds in basic configurations compared to high-speed TTL variants.^[28] The evolution of logic-level multiplexers began with discrete gates in the 1960s, where individual transistors and diodes formed basic switching circuits. By the early 1970s, integration advanced to medium-scale integration (MSI) chips, such as the 74LS151 series introduced in the early 1970s, consolidating multiple gates into single packages. This progressed to very large-scale integration (VLSI) by the 1980s, enabling millions of transistors on a chip for complex multiplexer arrays in CMOS technology.^[29][30]

Scalability Techniques

To scale digital multiplexers for larger input counts, one common technique is chaining or cascading smaller 2:1 multiplexers to form a 2^n:1 multiplexer. This approach involves connecting the output of one 2:1 multiplexer as an input to the next, requiring 2^n - 1 basic 2:1 units in total. Select lines are organized hierarchically, with the most significant bit controlling the top-level multiplexer and lower bits managing subgroups, enabling efficient expansion without exponential growth in control complexity.^[31] Another method employs multiplexer trees, structured as binary trees to reduce select line overhead and improve signal integrity. For instance, a 16:1 multiplexer can be built using five 4:1 multiplexers in a two-level tree: four in the first level, each handling four inputs (totaling 16), feeding into a fifth 4:1 multiplexer at the root, with select lines divided such that two bits control the lower level and the remaining two bits select among the intermediate outputs. This tree configuration minimizes the number of cascaded stages compared to linear chaining, thereby lowering propagation delay while distributing fan-out across levels.^[13] The Shannon expansion theorem further enhances scalability by demonstrating the multiplexer as a universal logic primitive for implementing any Boolean function. The theorem states that any function F can be decomposed with respect to a select variable S as: $$F = S \cdot F_1 + \bar{S} \cdot F_0$$F=S⋅F1​+Sˉ⋅F0​ where F_1 is the function with S=1, F_0 with S=0, and the overbar denotes complement. This recursive decomposition allows a 2^n:1 multiplexer to realize any n-variable function by connecting inputs to constants (0 or 1) or subfunctions, reducing the need for dedicated gates and enabling modular design of complex logic.^[32] These techniques offer key advantages over full decoder-based implementations for large-scale selection. Multiplexer trees and chaining typically require fewer gates than a decoder with AND-OR structure—while hierarchical select lines limit fan-out to O(log N) per gate, avoiding excessive capacitive loading that could degrade performance. However, delay analysis reveals logarithmic propagation (O(log N) stages) in trees versus linear in flat decoders, though fan-out constraints may necessitate buffering in deep trees to maintain signal integrity.^[33] A practical example is the use of a 256:1 multiplexer tree in memory addressing, where row and column decoders are augmented with tree-structured multiplexers to select one of 256 bit lines from a 2D array, reducing pin count and enabling compact integration in SRAM designs without a single massive decoder.^[34]

Demultiplexers

Fundamental Operation

A demultiplexer, often abbreviated as demux, is a combinational circuit that takes a single data input and routes it to one of multiple output lines, determined by the binary value applied to its select lines; it frequently includes an enable input to activate or disable the device. This setup allows the demultiplexer to function as a data distributor, directing the input signal exclusively to the selected output while keeping all other outputs inactive, typically at logic low.^[35] As the inverse of a multiplexer, a demultiplexer expands one input channel into several possible paths rather than consolidating multiple inputs.^[2] The core operation of a demultiplexer is based on an internal decoder that interprets the select lines as a binary address to enable one specific output path. For a basic 1-to-4 demultiplexer, two select bits (S1 and S0) control four outputs (Y0 through Y3), with the input signal I combined via AND gates to ensure it only appears on the addressed line when the device is enabled.^[36] If an enable signal E is present and asserted (E=1), the decoder generates a unique active-high signal for the corresponding select combination, gating the input to that output; otherwise, all outputs remain low.^[37] This decoder-driven mechanism ensures mutually exclusive activation, preventing signal conflicts across outputs. The behavior can be illustrated through a truth table for a 1-to-4 demultiplexer with enable, assuming active-high logic where the input I determines the output level on the selected line: Here, X denotes don't care.^[37] Mathematically, each output $Y_k$Yk​ is expressed as $Y_k = I \land D_k$Yk​=I∧Dk​, where $D_k$Dk​ is the decoder's minterm output for the select combination k (e.g., for Y0, $D_0 = \overline{S1} \land \overline{S0}$D0​=S1∧S0).^[36] In contrast to a multiplexer, which converges multiple inputs to one output, the demultiplexer reverses this flow by diverging one input to multiple potential outputs, altering the directionality of signal selection.^[35] This inverted input-output configuration makes demultiplexers particularly suitable for address decoding in digital systems, where select lines represent binary addresses to activate specific memory or peripheral devices.^[38]

Integrated Circuit Examples

One prominent example of a digital demultiplexer integrated circuit is the 74HC139, a dual 2-to-4 line decoder/demultiplexer from Texas Instruments' high-speed CMOS logic family. This IC operates across a supply voltage range of 2 V to 6 V and features typical propagation delays of 10 ns for enable-to-output and 12–14 ns for input-to-output at 5 V, enabling high-performance applications. It includes active-low enable inputs for easy cascading and provides four outputs per decoder section, with a maximum supply current of 80 μA, making it suitable for power-sensitive designs.^[39] Another widely used digital demultiplexer is the 74LS154, a 4-to-16 line decoder/demultiplexer from the low-power Schottky TTL series, originally developed in the 1970s as part of the 7400 family. It operates at a standard 5 V supply with typical propagation delays of 25 ns and includes strobe (enable) inputs to control output activation, supporting up to 16 mutually exclusive outputs for address decoding tasks. While lacking an integrated latch, variants like the 74HC4514 extend this functionality by incorporating address latches for storing select inputs, maintaining compatibility with 2 V to 6 V operation and propagation delays around 20 ns. For comparison, analog demultiplexers such as the 74HC4051 provide single-channel 8-to-1 switching, with digital control inputs operating from 2 V to 6 V and analog signals handling up to ±5 V or 10 V peak-to-peak, though digital variants like the above are preferred for pure logic routing due to lower on-resistance (typically 70 Ω) and minimal crosstalk. These ICs find practical use in memory address decoding, where the demultiplexer selects specific chip enables from a shared bus, and in LED display drivers, routing control signals to individual segments for multiplexed illumination.^[40] The 7400 series originated with TTL technology in the mid-1960s, offering robust performance but higher power consumption (up to 10 mW per gate), evolving in the 1970s and 1980s to low-power CMOS variants like the 74HC and later 74LVC families for reduced dissipation (under 1 μW static) and broader voltage compatibility. When selecting demultiplexer ICs, key criteria include the number of outputs (e.g., 4 for small-scale routing versus 16 for expanded addressing), presence of enable or strobe features for synchronization and cascading, and power dissipation (favoring CMOS for battery-powered systems over TTL's higher quiescent current). Modern equivalents in the SN74LVC family, such as the SN74LVC139A, extend this with 1.65 V to 3.6 V operation, propagation delays of 3.6 ns typical at 3.3 V, and inputs tolerant up to 5.5 V, addressing 2020s demands for low-voltage IoT and mobile applications.

Advanced Variants

Bidirectional Configurations

Bidirectional multiplexers facilitate data transmission in both directions across shared bus lines, distinguishing them from unidirectional variants by incorporating mechanisms for dynamic role reversal between inputs and outputs. This is typically achieved through the use of tri-state buffers arranged in a back-to-back configuration or integrated bidirectional switches, which allow signals to flow from port A to port B or vice versa under the control of a dedicated direction (DIR) signal.^[41] Such designs ensure that only one direction is active at a time, preventing conflicts on the bus while maintaining signal integrity across voltage levels from 2 V to 6 V in CMOS implementations.^[42] In operation, an additional control line—often labeled DIR or combined with a select enable—determines the data flow direction, enabling the multiplexer to toggle between transmit and receive modes. For instance, an 8-bit bidirectional multiplexer can emulate I2C bus functionality by selecting among multiple downstream channels while handling bidirectional open-drain signaling on SCL and SDA lines, supporting data rates up to 400 kHz.^[43] The conceptual behavior for a single-bit path is represented as $Y = I$Y=I when DIR = 1 (output drives input), with the output entering a high-impedance tri-state condition otherwise to allow bidirectional isolation.^[44] These configurations offer significant advantages in bidirectional bus systems, such as reduced component count by combining buffering, switching, and direction control in a single IC, which lowers power consumption to as low as 80 μA maximum and simplifies PCB layouts.^[44] However, challenges include avoiding bus contention, where simultaneous activation of multiple drivers could cause voltage spikes or latch-up; this requires precise timing of control signals and often pull-up resistors for open-drain compatibility.^[41] Prominent integrated circuit examples include the 74HC245 octal transceiver from NXP, which provides 3-state bidirectional buffering for 8 data lines with separate output enable (OE) and DIR pins, operating across 2 V to 6 V supplies.^[42] For analog or mixed-signal applications, Texas Instruments' TMUX1208 serves as an 8:1 bidirectional multiplexer supporting signals up to 5.5 V and a bandwidth of 65 MHz.^[45] In I2C-specific scenarios, NXP's PCA9540B acts as a dual-channel bidirectional multiplexer, enabling seamless switching between two I2C buses for multi-device networks.^[43] Historically, devices like the 74LS245 (TTL predecessor to 74HC245) were widely employed in 1980s microcomputer designs, such as those in Mostek systems, to manage asynchronous bidirectional data buses between processors and peripherals.

Use in Programmable Logic

In programmable logic devices (PLDs), multiplexers serve as fundamental building blocks, particularly in field-programmable gate arrays (FPGAs), where they form the core of lookup tables (LUTs) that implement arbitrary Boolean functions. A LUT essentially functions as a configurable multiplexer tree, with SRAM bits stored at the inputs representing the truth table for the desired logic operation; for instance, a 4-input LUT can realize any of the 65,536 possible 4-variable Boolean functions by selecting the appropriate output from a 16-entry memory array via multiplexers controlled by the inputs. This structure allows FPGAs to emulate diverse combinational and sequential logic without fixed wiring, providing flexibility in circuit design.^[46][47] Configuration in these devices relies on SRAM-based multiplexer arrays within logic blocks, where configuration bits dynamically select inputs to combinational logic elements. In Xilinx FPGAs, for example, a configurable logic block (CLB) typically includes multiple 4:1 or 6:1 LUTs implemented as cascaded 2:1 multiplexers, with SRAM cells at the leaves of the tree determining the function; the select lines are driven by input signals or configuration data loaded during initialization. This setup enables rapid reprogramming via bitstream files, contrasting with one-time programmable alternatives like fuses.^[48][49][50] The use of multiplexers in PLDs traces back to the 1970s with programmable array logic (PAL) devices, which employed fixed AND arrays feeding programmable OR multiplexers for sum-of-products logic, offering initial reconfigurability over custom ASICs. Evolving into modern FPGAs by the 1980s and advancing significantly post-2000 with larger, faster architectures, this approach provides key advantages such as field reconfigurability, enabling ASIC emulation for prototyping and verification without fabrication costs or delays—commercial FPGA platforms can achieve emulation speeds up to 5 MHz for complex designs. Such versatility supports iterative design cycles and hardware acceleration in applications like signal processing.^{[51][52][53][54]} To handle scaling in large FPGAs, hierarchical multiplexer structures are employed in routing fabrics, organizing interconnects into local, global, and long-line segments where pass-transistor or multiplexer-based switches form tree-like networks to connect thousands of logic blocks efficiently. This reduces wiring congestion and delay compared to flat architectures. In 2020s advancements, emerging programmable logic extends to photonic domains, with optical FPGAs using reconfigurable multiplexers for wavelength-selective routing in silicon photonic circuits, enabling high-speed, low-power processing for data centers. As of 2025, hypermultiplexed integrated photonic processors using space-time-wavelength multiplexing have demonstrated trillions of operations per second for AI and data center applications.^[55][56][57]

Specialized Uses

Arithmetic Circuitry Applications

Multiplexers provide a versatile approach to implementing arithmetic operations in digital circuits, particularly for adders, where they can replace traditional gate-based designs to generate sum and carry outputs. A 1-bit full adder can be implemented using multiplexers; for example, the sum output uses a 2:1 MUX with inputs A XOR B and NOT(A XOR B), selected by the carry-in bit to compute (A XOR B) XOR Cin. The carry output requires additional logic or MUXes to compute (A AND B) OR (Cin AND (A XOR B)). A novel design uses six 2:1 multiplexers to implement the full adder with only 12 transistors.^[58] This configuration leverages the multiplexer's selection mechanism to handle the truth table logic efficiently, reducing the need for multiple XOR and AND gates. For multi-bit adders, such as a 4-bit ripple-carry design, these 1-bit mux-based full adders are cascaded, with the carry-out of each stage feeding into the next, enabling straightforward extension while maintaining modularity.^[58] Beyond adders, multiplexers play a key role in multiplier architectures, especially those employing Booth encoding, where arrays of 2:1 or 4:1 multiplexers select and shift partial products based on overlapping bit groups of the multiplier. In a radix-4 Booth multiplier, for instance, each multiplexer chooses between multiples of the multiplicand (0, ±1, or ±2 times) according to the encoded bits, followed by accumulation via adders, which reduces the number of partial products compared to array multipliers and improves speed.^[59] This mux-centric approach is particularly advantageous in signed multiplication, as it inherently handles sign extension through the selection logic. One benefit is gate efficiency; a mux-based full adder cell, for example, uses only 12 transistors versus 28 in a standard static CMOS design, leading to lower power dissipation and area savings in dense arithmetic blocks.^[58] In arithmetic logic units (ALUs) within CPU designs, multiplexers serve as operation selectors, routing inputs to functional units for tasks like addition or subtraction and then choosing the appropriate output. A typical 4-bit ALU might use a 2:1 multiplexer to select between an adder output and a subtracted result (generated via two's complement), controlled by an operation code bit, allowing a single hardware path to handle multiple arithmetic functions efficiently.^[60] This integration minimizes wiring complexity and supports scalable designs in processors. Historically, during the 1970s and 1980s, such mux-based techniques were pivotal in early VLSI arithmetic units, enabling compact implementations that maximized transistor density in pioneering integrated circuits like those in signal processing chips.^[61] In contemporary field-programmable gate arrays (FPGAs), optimizations exploit multiplexers within configurable logic blocks to enhance arithmetic performance, such as by embedding fast muxes in carry chains for reduced latency in adders and multipliers.^[62]

Emerging Implementations

In telecommunications, optical multiplexers based on wavelength-division multiplexing (WDM) have advanced significantly, enabling the simultaneous transmission of multiple data streams over a single optical fiber to meet surging bandwidth demands. These systems utilize arrayed waveguide gratings (AWGs) to spatially separate and combine wavelengths with high precision, typically operating in the C-band (around 1550 nm) for minimal attenuation in silica fibers. Advancements in AWG design have achieved low insertion losses and low crosstalk, supporting dense integration in photonic integrated circuits. Low-loss multimode-output AWGs further enable compact WDM receivers, integrating photodetectors for error-free operation at 25 Gb/s per channel in multi-wavelength systems.^[63] Quantum multiplexers represent a frontier in qubit routing for scalable quantum processors, leveraging superconducting or photonic elements to manage control signals and interconnects amid wiring constraints. Superconducting implementations employ multiplexed architectures with shared row and column control lines, allowing a single microwave source to address multiple transmon qubits, thereby reducing cryogenic cabling while maintaining coherence times exceeding 100 μs. Photonic quantum multiplexers, often using time-bin or wavelength encoding, facilitate hybrid interfaces between superconducting qubits and optical networks, enabling distributed quantum computing with fidelity above 90% for qubit-photon entanglement.^[64] Post-2015 research highlights time-multiplexed control schemes that sequence qubit operations, though they introduce computational overhead of 20-30% due to sequential addressing. At the nanoscale, memristor-based multiplexers offer a pathway beyond CMOS limitations in neuromorphic computing, where crossbar arrays function as reconfigurable routers for spike transmission in spiking neural networks. These devices exploit resistive switching in materials like HfO₂ to enable high-density and low-energy switching, surpassing CMOS interconnects in power efficiency for edge AI applications.^[65] By emulating synaptic routing, memristor crossbars enable in-memory computation, reducing latency in asynchronous neuromorphic systems compared to traditional von Neumann architectures. However, scaling to arrays larger than 128×128 encounters IR drop and leakage issues, limiting fan-out to 64 without active compensation.^[65] Integration of multiplexers in AI and machine learning hardware has surged in the 2020s, with dynamic routing mechanisms optimizing data flow in accelerators for adaptive neural networks. In tile-based architectures, multiplexers within processing elements selectively route activations and weights, supporting sparse computations in transformers and achieving up to 4× throughput gains over static designs in inference tasks. This enables real-time resource allocation in edge devices, as seen in RISC-V SoCs with embedded streaming accelerators that multiplex data paths for CNN and GNN workloads.^[66] Scalability challenges persist across these domains, particularly in quantum multiplexers where noise from decoherence and crosstalk degrades fidelity, as evidenced by IBM's 2023 prototypes demonstrating error rates below 0.1% per gate only after advanced mitigation techniques.^[67] Efforts like error-corrected routing in IBM's Heron processor aim to extend circuit depths to 5,000 two-qubit operations, underscoring the need for hybrid classical-quantum control to overcome thermal and environmental noise barriers. As of November 2025, IBM released updated quantum processors, including the 120-qubit Quantum Nighthawk, advancing toward fault-tolerant systems by 2029.^[68]